1. Field of the Invention
The present invention relates to a drive-force transmitting mechanism that is used for switching operation modes of apparatus such as a compact disk (CD) play-back apparatus and a VTR, and more particularly to a drive-force transmitting mechanism that permits and does not permit transmission of a torque at a predetermined timing.
2. Description of the Related Art
FIG. 11 illustrates a conventional drive-force transmitting mechanism, and particularly a pertinent portion of a cassette loading apparatus disclosed in Laid-open Japanese Patent (KOKAI) No. 11-219555.
A cam gear 102 is journaled on a chassis 101 and is in mesh with a worm gear 105. The rotation of a motor 103 is transmitted through a belt 104 to the worm gear 105, which in turn drives the cam gear 102 in rotation.
A capstan motor 106 generates a torque, which is transmitted through a pulley 109 and a belt 107 to a gear pulley 108. A lever 110 is pivotally supported on the chassis 101 at a pivot shaft 110c. The lever 110 has a cam pin 110a formed at a midway point of the lever 110 and a pin 110b formed at a free end thereof. The cam pin 110a engages a cam groove 102a formed in the cam gear 102.
A slide plate 111 is formed with a cutout 111a therein that receives the pin 110b and is slidably supported on the chassis 101. When the lever 110 is driven by the cam gear 102 to pivot about the pivot shaft 110c, the pin 110b causes the slide plate 111 to move back and forth in the X direction. The slide plate 111 is formed with a cam surface 111b on one longitudinal end thereof.
A lever 113 is rotatably supported at a midway point thereof on the chassis 101 and rotates relative to the chassis 101 about a pivot shaft 113a. The lever 113 has one longitudinal end thereof connected to a tension spring 115 and the other end rotatably supported on a gear pulley 114. The lever 113 also has a pin 113b provided thereon between the spring 115 and the pivot shaft 113a. The spring 115 urges the pin 113b against the cam surface 111b counterclockwise.
A belt 118 is entrained about the gear pulley 114 and an intermediate gear 116. The intermediate gear 116 is in mesh with a drive gear 117 that is rotatably mounted on the chassis 101. The rotation of the gear pulley 114 is transmitted through the intermediate gear 116 to the drive gear 117. The drive gear 117 drives a cassette loading mechanism, not shown.
The operation of the conventional clutch of the aforementioned constriction will be described.
When a user inserts a cassette 120 into the apparatus, a detection switch, not shown, detects the cassette 120 and then the drive motor 103 runs to rotate the cam gear 102 to bring the apparatus into a predetermined mode of operation. As the cam gear 102 rotates, the lever 110 pivots counterclockwise, causing the slide plate 111 to move in the X direction away from the origin O. Thus, the pin 113b is guided on the cam surface 111b to rotate counterclockwise so that the gear pulley 114 moves into meshing engagement with the gear pulley 108.
Then, the capstan motor 106 starts to rotate. The rotation of the capstan motor 106 is transmitted through the gear pulleys 108 and 114, belt 118, intermediate gear 116, to the drive gear 117. The drive gear 117 drives the cassette-loading mechanism to pull in the cassette 120 into the apparatus, thereby placing the cassette 120 on the reels 121 and 122.
The detection switch, not shown, detects when the loading operation is completed, and the capstan motor 106 stops rotating and the drive motor 103 rotates in the reverse direction. Thus, the slide plate 111 is moved in the X direction toward the origin O, so that the gear pulley 114 moves out of meshing engagement with the gear pulley 108. Then, a tape loading mechanism, not shown, draws out the tape from the cassette 120 and loads it onto a rotary drum, not shown. The capstan motor 106 then rotates to run the tape for the reproduction operation.
FIG. 12 illustrates another conventional clutch mechanism, a commonly used geneva mechanism.
Referring to FIG. 12, a drive gear 151 has a gear portion 151a and a non-gear circumferential portion 151b having a smooth circumferential surface. A driven gear 152 has gear portions 152a and fish-tail-shaped portions 152b, the gear portion 152a and the fish-tail-shaped portion 151b being arranged alternately. The gear portion 151a meshes with the gear portion 151a. 
When the gear portion 151a is in mesh with the gear portion 151a, the driven gear 152 rotates so that the rotation of the drive gear 151 is transmitted to the driven gear 152. When the non-gear circumferential portion 151b moves into contact engagement with the fish-tail-shaped portion 151b, the rotation of the drive gear 151 is not transmitted to the driven gear 152. As the drive gear 151 further rotates, the gear portion 151a again moves into meshing engagement with the gear portion 151a so that the rotation of the drive gear 151 is transmitted to the driven gear 152. In this manner, the continuous rotation of the drive gear 151 is transmitted intermittently to the driven gear 152.
The drive-force transmitting mechanism disclosed by Laid-open Japanese Patent (KOKAI) No. 11-219555 suffers from the problem that the drive motor 103 is required as a drive source that drives the clutch to engage and disengage. The need for such a drive source leads to an increase in cost.
The drive-force is transmitted or not transmitted by bringing the gears into or out of meshing engagement with each other, respectively. When the gears are rotating, the gears are not only smoothly brought into or out of meshing engagement but the gear teeth may be damaged.
The geneva mechanism requires no special drive source for engaging and disengaging the gears. However, the gears must be closely located to each other so that they move into and out of meshing engagement with each other as the drive gear rotates. In other words, the drive gear cannot be disposed away from the driven gear. Thus, the geneva mechanism is not practical in a case where the relative distance between the drive side and the driven side changes depending on whether the clutch is engaged or disengaged.
An object of the invention is to provide a drive-force transmitting mechanism that requires no drive source such as a motor for driving the clutch to engage and disengage.
Another object of the invention is to provide a drive-force transmitting mechanism that transmits a drive force irrespective of whether the relative distance between the drive side and the driven side changes depending on the engagement state of the drive-force transmitting mechanism.
A drive-force transmitting mechanism engages to transmit the rotation of a first disk to the second disk and disengages not to transmit the rotation. A first disk is rotatable about an axis. A second disk is rotatable about the axis and has a first engagement member formed thereon. A second engagement member is mounted on the first disk such that the second engagement member is sandwiched between the first disk and the second disk, the second engagement member being movable toward the axis or away from the axis. A guide member guides the second engagement member such that the second engagement member moves radially toward the axis or away from the axis depending on a direction in which the first disk rotates about the axis. When the second engagement member engages the first engagement member, rotation of the first disk is transmitted to the second disk. When the second engagement member disengages from the first engagement member, rotation of the first disk is not transmitted to the second disk.
When the first disk rotates in a first direction through a first angle range, the guide member guides the second engagement member to move radially toward the axis so that the second engagement member engages the first engagement member. When the first disk rotates in a second direction opposite to the first direction through a second angle range subsequent to the first angle range, the first disk and the second disk rotate together so that rotation of the first disk is transmitted to the second disk. When the first disk rotates in the first direction through a third angle range subsequent to the second angle range, the second engagement member disengages from the first engagement member so that rotation of the first disk is not transmitted to the second disk.
The guide member has a cam groove formed therein and the second engagement member has a guide pin that engages the cam groove, the guide pin being guided along the cam groove when the first disk rotates about the axis.
The guide pin is pivotal about a position on a radius of the first disk. The cam groove has a first arcuate groove having a large diameter, a second arcuate groove having a medium diameter, a third arcuate groove having a small diameter, a first radially extending groove that connects the first arcuate groove and the second arcuate groove together, and a second radially extending groove that connects the second arcuate groove and the third arcuate groove together.
The engagement member is one of two engagement members disposed on the first disk and diametrically opposite with respect to the axis. The drive-force transmitting mechanism further comprises a coupling member that engages the two engagement members to transmit movement of one of the two engagement members to the other of the two engagement members such that the two engagement members operatively move toward and away from the axis.
One of the two engagement members is mounted on a first lever that is pivotally mounted to the first disk and the other of the engagement members is mounted on a second lever that is pivotally mounted to the first disk.
The coupling member is pivotal about the axis and pivotally engages the first lever and the second lever.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.